Role of metal ions in reactions catalyzed by pig heart triphosphopyridine nucleotide-dependent isocitrate dehydrogenase. II. Effect on catalytic properties and reactivity of amino acid residues.
نویسنده
چکیده
The TPN-specific isocitrate dehydrogenase of pig heart, which is here shown not to contain zinc or manganese as essential constituents, is most effectively activated by divalent manganous ions. On the basis of the effect of isocitrate concentration on the apparent Michaelis constant for manganous ion and the reciprocal influence of manganous ion concentration on the apparent Michaelis constant for isocitrate, as well as the results of studies of the direct binding of manganous ion and isocitrate (Colman, R. F., Biochim. Biophys. Ado, (1969) 191, 469; Villafranca, J. J., and Colman, R. F. (1972), J. Biol. Chem., 247, 209), it is concluded that the metal-isocitrate complex is the actual substrate for the enzyme. Significant activation is exhibited by divalent manganous, cadmium, zinc, cobaltous, and magnesium ions; whereas calcium and strontium function as competitive inhibitors with respect to manganese. The first five metals exhibit differential ability to enhance the rate of the over-all oxidative decarboxylation of isocitrate, decarboxylation of oxalosuccinate, over-all reductive carboxylation of oc-ketoglutarate and reduction of oxalosuccinate. The metals also differ in their ability to influence the course of chemical modification of the enzyme by diazo-IH-tetrazole. Manganous ion potentiates the inactivation by the reagent by increasing the availability of lysyl residues; zinc and cadmium increase the inactivation by the reagent but do so by altering the reactivity of residues other than lysyl residues; and magnesium and cobaltous ions do not observably influence the modscation reaction. It is concluded that the catalytic activity and the conformation of isocitrate dehydrogenase is determined in part by the particular metal which is functioning as activator.
منابع مشابه
A glutamyl residue in the active site of triphosphopyridine nucleotide-dependent isocitrate dehydrogenase of pig heart.
The maximum velocity of the reaction catalyzed by the pig heart TPN-specific isocitrate dehydrogenase depends on the basic form of an enzymatic group of pK 5.7. This pK is independent of temperature from 10-30” and increases in 20% ethanol, suggesting the ionization of a carboxyl group. The enzyme is inactivated by incubation at pH 7.0 with 1 cyclohexyl3 (2 morpholinoethyl) carbodiimide either ...
متن کاملKinetic evidence for the dimerization of the triphosphopyridine nucleotide-dependent isocitrate dehydrogenase from pig heart.
متن کامل
Isocitrate dehydrogenase from bovine heart: primary structure of subunit 3/4.
Bovine NAD(+)-dependent isocitrate dehydrogenase was shown previously to contain four subunits of approx. 40 kDa (subunits 1-4) possessing different peptide maps and electrophoretic properties [Rushbrook and Harvey (1978) Biochemistry 17, 5339-5346]. In this study the heterogeneity is confirmed using enzyme purified by updated methods and from single animals, ruling out allelic variability. Sub...
متن کاملDi- and triphosphopyridine nucleotide isocitric dehydrogenases in yeast.
The biological conversion of d-isocitric to a-ketoglutaric acid was established by the work of Martius and others (1-4). Adler et al. showed that, with extracts of acetone powders of animal tissues, triphosphopyridine nucleotide (TPN) is a specific coenzyme in the reaction and cited evidence for a similar specificity in yeast. Ochoa (5) synthesized oxalosuccinic acid, the intermediate postulate...
متن کاملIsolation and some properties of the triphosphopyridine nucleotide isocitrate dehydrogenase from Bacillus stearothermophilus.
The TPN+-dependent isocitrate dehydrogenase from Bacillus stearothermophilus (NCA 2184) has been isolated and purified approximately lOOO-fold. The preparation described is homogenous as judged by sedimentation equilibrium and disc gel electrophoresis. The weight average molecular weight estimated by sedimentation equilibrium analysis is 92,500. In 6 M guanidine hydrochloride-l mM dithiothreito...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
- The Journal of biological chemistry
دوره 247 1 شماره
صفحات -
تاریخ انتشار 1972